1. Field of the Invention
The field of the invention is that of parallelism measuring devices. More specifically the field is that of anode-cathode parallelism gap gauges.
2. Prior Art
The technique typically used to gauge parallelism and distance between anodes and cathodes in reactive etching chambers is that of compressing clay. Using this method clay balls are placed on an anode and the cathode is lowered towards the anode until the cathode touches the clay balls and compresses them. The clay figures produced by this prior art method are then measured in order to gauge the position of the anode and cathode at the various clay ball locations. Measuring the clay figures to determine the distance between the anode and cathode is an indirect measurement. This level of indirection compounds measurement errors.
The problems with this method include the indirect measurement, the imprecision of the clay balls as a measuring instrument, and the deposition of clay upon the anode and the cathode. The clay balls, after being pressed, may expand or contract, thereby distorting the measured value. The deposition of the clay on the anode and cathode requires that they be cleaned. The presence of clay oils or cleaning materials requires airing out the chamber for hours after the clay measurements. Also, clay is elastic so that the clay can spring back, destroying the accuracy of the measurement. The changing temperature of the clay can change the measured results. In addition, clay ball tests can not be repeated to test the accuracy of the initial measurement.
It is important to keep the anode and cathode relatively parallel for best results in an etching chamber. Also, it is necessary to check the distance between the anode and cathode independently of the chamber's instruments to guarantee proper calibration of the chamber.
What is needed is a parallelism gauge that both provides for accurate, direct measurement of the parallelism of and distance between the anode and the cathode. Also, what is needed is a parallelism gap gauge that avoids deposition of contaminating foreign particles upon the surfaces. One object of the present invention is to provide such an accurate parallelism gap gauge. Another object of the present invention is to provide a parallelism gap gauge that does not contaminate either of the surfaces measured.